It came out of the male hydraulic coupler on a takeuchi skid steer..
Stucchi does sell seal kits for male flat face couplers, new couplers aren’t outrageously expensive either though.
Have you looked into seal websites? Hydrapak and York Seals have some easy to decipher sites and catalogs. I've not had as much luck with Hercules but they have plenty to offer as well. Get a set of calipers to do your measurements.
unfortunately the quick coupler market has moved like a lot o things to throwaway stuff. stick with a good brand Parker, Stucchi, Faster etc and it will likely be less bother to find a whole coupler than a seal kit.